Heat pipe heat exchangers are well known in the field of heat recovery and dehumidification. Heat pipes rely on a phase change process to absorb heat by evaporation and release heat by condensation, transferring large amounts of heat energy with very little difference in temperature.
Heat pipes typically comprise a condenser and an evaporator connected to each other in a closed system. The typical heat pipe comprises an enclosed tube system having one end forming an evaporator portion and having another, somewhat-cooler and lower-pressure end forming a condenser portion.
In use, liquid refrigerant present in the evaporator portion is heated by the environment, vaporized, and rises into the condenser portion. In the condenser portion, the refrigerant is cooled by the environment, is condensed with the release of heat, and is then returned to the evaporator portion. The cycle then repeats itself, resulting in a continuous cycle in which heat is absorbed from the environment by the evaporator and released by the condenser.
Heat pipe heat exchangers are generally made into two sections that are inserted, each in one of two air streams, where there is a temperature differential between the two air streams. The air streams are preferably in close proximity to each other and preferably flow in opposite directions. The flow of the refrigerant in heat pipes can be induced by passive techniques such as gravity flow, capillary action, thermal pumping, and thermo-syphoning. Such passive techniques have dimensional restrictions, and work better in relatively small heat pipes. Thus, there is a need for a design which works well for larger scale heat pipes, and for heat pipes that transfer heat between a hot source or air stream located higher than the cold source.
A heat pipe loop includes a first heat pipe section having a first temperature and a second heat pipe section having a second temperature higher than, the first temperature. The first heat pipe section is a condenser and the second heat pipe section is an evaporator. A vapor line connects an upper portion of the first heat pipe section with an upper portion of the second heat pipe section. A liquid line connects a lower portion of the first heat pipe section with a lower portion of the second heat pipe section. In one embodiment, the first heat pipe section is disposed at a first elevation and the second heat pipe section is disposed at a second elevation higher than the first elevation. A pump directs liquid from the first heat pipe section to the second heat pipe section through the liquid line.